Flexible heat barrier and fire shelter for wildland firefighters made therefrom

ABSTRACT

A flexible heat barrier is configured to absorb and deflect heat energy and utilizes a multilayer construction wherein each layer provides a specific purpose. An outer layer configured for exposure to a heat flux includes a coating having an intumescent component and an opacifier component. An inner layer includes a foil that may include a high emittance coating to more effectively reflect radiation. A middle layer includes an insulating fabric layer that may include oriented fibers that can effectively polarize radiation and may include a plurality of layers of oriented fibers that are configured at an offset angle to deflect and reduce radiation transmission through the middle layer. A flexible heat barrier may also include a flexible gas barrier that includes a phase change material, such as frits that melt at a predetermined temperature and flow into gaps to reduce the permeability and further block heat flux.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part application of U.S. Application No. 17/916,794, filed on Oct. 3, 2022 and currently pending, which is a national stage application of PCT application No. PCT/US22/11870, filed on Jan. 10, 2022, which claims the benefit of priority to U.S. Provisional Pat. Application No. 63/298,168, filed Jan. 10, 2022, provisional patent application No 63/134,977, filed on Jan. 8, 2021, and provisional patent application No 63/134,975, filed on Jan. 8, 2021, and this application is a continuation in part of U.S. Pat. Application No. 17/572,619 filed on Jan. 10, 2022 and currently pending, and this is a continuation in part of PCT application No. PCT/US23/10428, filed on Jan. 9, 2023; the entirety of all applications are hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a flexible heat barrier configured to absorb and deflect heat energy and applications of said flexible heat barrier including fire shelters for wildland firefighters and aerospace entry vehicle shields.

Background

Wildland firefighters are on the front line of fighting wildfires. They cut and remove burning material to slow or stop the fire and conduct backburning for the same purpose. Unfortunately, these firefighters sometimes are overtaken by a fast moving wildfire, such as when the wind changes direction. When they are trapped and can not escape from the approaching fire, their last resort is to deploy a fire shelter and take cover within the shelter. Efforts have been made to make these portable and emergency fire shelters lighter in weight, smaller in volume and more capable of deflecting flame fronts and high temperatures.

The frequency and intensity of these emergency fire fighter situations where a fire shelter is required is increasing due to climate change, which is causing drier conditions that drive hotter fires that are more difficult to control. Wildland firefighters are needed to save civilian lives, protect structures, and safeguard national treasures like the General Sherman Tree in Sequoia National Park. Firefighters carry a fire shelter to protect themselves if they are trapped by a burning fire, but the efficacy of the shelter is limited by the amount of gear the firefighters carry. Although different types of firefighters carry different amounts of gear, Hot Shots, for example, often hike long distances, work long shifts, and often carry more than 20.4 kg (45 lbs), including the fire shelter. A heavier/bulkier fire shelter would provide better protection but would also impede their ability to do their job and increase fatigue, which could ultimately endanger more firefighters.

The M2002 fire shelter, available from the U.S. Forest Service weighs 2.0 kg (4.4 lbs), occupies 3.44 kcm³ (210 in³) and provides approximately 54 seconds of protection in simulated fire exposures. The design replaced a single wall fire shelter that was developed in the 1970′s, which provided approximately 15 seconds of protection. The current M2002 fire shelter prevents serious injury or death approximately 90% of the times it is deployed.

The M2002 fire shelter met all the original criteria set by the U.S. Forest Service and included a multilayer construction, including an outer layer made of woven silica cloth laminated to 1.0 mil aluminum foil, referred to as the outer layer. The foil on the outside reflects radiant heat and absorbs heat when it finally melts as the flames reach the shelter. The adhesive that holds the foil to the fabric decomposes without adding heat or toxic gasses. The silica fabric slows the rate of heat transfer to the inside of the shelter, as does the small gap between the outer layer and inner layer. The inner layer is made of a lightweight, fiberglass fabric laminated to aluminum foil. In this layer, the foil faces the inside of the shelter such that as the temperature of the inner surface increases, less heat is radiated within the shelter to heat the occupant. The foil also provides a barrier to keep flammable gasses, toxic fumes and/or smoke from contaminating the breathing air of the shelter occupant. The new design also includes a floor to provide structural integrity and seal out smoke, seams that are designed to stiffen the shelter structure such that it will maintain its shape even after the foil burns off the outer layer, and special handles on the long side of the shelter such that the shelter can be quickly deployed with a few ‘shakes’. The M2002 fire shelter was first available through General Services Administration (GSA) in June of 2003.

A portable fire shelter that has improved heat barrier properties and/or reduced weight would be of great value to the U.S. Forest Service to protect our wildfire firefighters.

SUMMARY OF THE INVENTION

The invention is directed to a flexible heat barrier a flexible heat barrier configured to absorb and deflect heat energy and applications thereof, including fire shelters for wildland firefighters and heat shield for aerospace entry vehicles. The improved portable fire shelter utilizes new materials that enable improved fire, flame, radiant heat and temperature protection at a lower weight.

A flexible heat barrier may include a plurality of layers, each with a specific purpose and configuration with respect to the heat or flame exposure. An insulating fabric layer may be configured between an outer coating and an inner foil component. The fabric layer may include high temperature fibers woven to reduce hot gas flow into the surface and/or as an opacifier to attenuate radiative heat transfer in addition to satisfying mechanical requirements. The fibers of the insulating fabric layer may be oriented to provide polarization of the radiant energy. A coating may be coupled to the insulating fabric layer and extend on an exposure side of the flexible heat barrier. The coating may include a particular arrangement of materials to reduce the permeability of the flexible heat barrier, provide heat capacitance and deflect or reflect heat from the flexible heat barrier. A foil may be coupled to the insulating fabric and may form the shield side of the flexible heat barrier, or inner layer when formed into a portable fire shelter.

A flexible heat barrier may include a coating that may be coupled to the insulating fabric layer and configured as the exposed layer (exposed to flames, high winds, abrasion, etc.) of the flexible heat barrier, configured for exposure to the incident heat. Or it may be configured as an element within a Thermal Protection System that includes other elements designed to provide other specific benefits not covered herein. The coating may be configured for absorbing and deflecting heat and reducing airflow through the flexible heat barrier. An exemplary coating may include an intumescent component that expands with heat to increase the volume of the coating during exposure to heat and/or flame, an opacifier component, such as high temperature fibers, a gas barrier component that reduces the permeability of the flexible heat barrier and a binder to hold the various materials together and/or bond the coating to the insulating fabric layer.

A flexible heat barrier may include a metal foil that is configured opposite the coating from the insulating fabric and on a shield side of the flexible heat barrier. The shield side forms and interior side of the fire shelter, or occupant side, opposite the direction of heat source or flame. A metal foil may be titanium as it has very high temperature capability and lower density than other metals, and the foil may include a gold coating to reduce emissivity, or it may be aluminum foil with its advantages of low cost and ready availability. Aluminum has an emissivity of about 0.3 in the oxidized form at a temperature of 400° C. and gold has an emissivity of about 0.01 to 0.1 at a temperature of 400° C. The gold may vapor deposited on a foil, such as aluminum or titanium and may be very thin, such as about 1,500 µm or less, or 1,000 µm or less, or 700 µm or less and any range between and including the thickness values provided. Put another way, a foil may have a first layer that has a first emissivity and a second layer that has an emissivity that is at least half the emissivity of the first layer at a temperature of 400° C. The second layer may be a vapor deposited layer on the first layer and may be very thin, having a thickness that is a fraction of the first layer thickness, such as a quarter or less, a tenth or less, a twentieth or less, a hundredth or less or less. The thickness of the second layer may be about ,500 µm or less, or 1,000 µm or less, or 700 µm or less and any range between and including the thickness values provided.

An exemplary flexible heat barrier includes each of the three layers, the insulating fabric layer with the coating configured on an exposure side and a metal foil configured on a shield side of the flexible heat barrier. Additional layers of material or components may be included in the flexible heat barrier, such as

-   a. a phase change material, a material that melts and flows to     absorb heat and reduce permeability of the flexible heat barrier. -   b. Vermiculite, a natural material that occurs in platelets which     may align to reduce advection through the flexible heat barrier -   c. Opacifiers, particles or whiskers with optical properties chosen     to attenuate radiative heat transfer through the flexible heat     barrier -   d. Intumescent materials, that expand and absorb heat as they are     heated

A fire shelter made with the flexible heat barrier may have improved survivability time, as described herein and may be light weight. The coating aids in deflecting and absorbing the heat and flame, while the insulating layer provides strength and can be configured with an opacifier or may polarize the radiant energy to reduce heat transmission through the flexible heat barrier. The metal foil on the shield side of the flexible heat barrier is a reflective shield component that may include materials with low emissivity to reflect radiant heat back away from the shield side.

An exemplary fire shelter may be designed with curved surfaces and minimal surface-area-to-volume ratio to reduce radiant heat absorption and avoid causing fires near deployed shelters. An exemplary fire shelter may allow the occupant to lie face-down to breathe cooler, smoke-free air. An exemplary fire shelter may utilize materials selected to optimize strength, thermal protection, radiant heat resistance, flammability resistance, toxic outgassing and combustion products and durability to folding and unfolding for deployment.

An exemplary fire shelter has an upper shell portion and a floor portion configured to extend over the ground when deployed. The upper shell portion includes a shell fabric that may be constructed using the flexible heat barrier described herein. The shell fabric may be durable and have effective strength for the portable fire shelter application, including resisting high winds that are common with approaching fires. The shell fabric may have an average burst strength, for three specimens, of not less than 482 kPa (70 psi) when tested per ASTM D 774 and Paragraph 4.4.2.7 of the United States Department of Agriculture (USDA) specification. Also, the shell fabric may have a tensile strength of about 157 N/cm (90 lbf/in) or more, or about 210 N/cm (120 lbf/in) or more, according to USDA Forest Service Specifications 5100-607D and tested according to ASTM D5034-21 Standard Test Method for Breaking Strength and Elongation of Textile Fabrics (Grab Test).

Insulating Fabric Layer

The flexible heat barrier includes an insulating fabric layer having an array of high temperature fibers such as those shown in Table 1. The fibers may be woven or non-woven fibers and may have a melt temperature of at least 800° C. or more, and preferably 1000° C. or more, or even 1200° C. or more. The fibers may be inorganic fibers such as silicon carbide, glass, fiberglass, quartz and the like. The fibers may also be carbon fibers. The fibers may be carbon fibers that are subsequently converted to silicon carbide in situ. The fibers may include polymeric fibers such as polyimide fibers that have a melt temperature of above 350° C. and which might aid in absorbing heat from a flame front that moves over a fire shelter. A blend of any of the fibers described herein may be included in the insulating fabric layer, or a layer of the insulating fabric layer. The fibers may be long having a length to diameter ratio of about 50:1 or more, 100:1 or more or even 1000:1 or more. The fibers may have a denier of about 20 or less, about 10 or less, about 5 or less, about 2 or less, about 1 or less. The lower the denier, the higher the surface area which may aid in scattering the heat and also polarizing the radiant energy.

The insulating fabric layer may include one or more layers of oriented high temperature fibers that include fibers that are aligned with each other, parallel along the length of the fibers and having a spacing or gap therebetween. The aligned oriented high temperature fibers may have a spacing between the aligned or oriented fibers of about 5 µm or less, about 3 µm or less, about 2 µm or less, about 1 µm or less or even about 0.5 µm or less. The closer the spacing is to the wavelength of the incident radiation, the better the polarizing effect may be. Also, an insulating fabric layer may include a plurality of oriented high temperature fiber layers that are configured at offset angles to each other, or orthogonally to each other. A first layer of insulating fabric layer may include oriented high temperature fibers that are oriented substantially orthogonally to a second and adjacent layer of oriented high temperature fibers, within about 20 degrees of orthogonality.

Also, a first layer and second layer may have different spacing between the aligned or oriented fibers to account for temperature changes through the thickness of the flexible heat barrier. A first layer, configured more proximal to the exposure side may have a smaller spacing between fibers than a second layer configured more proximal to the shield side. The second layer spacing between oriented fibers may be greater by about 20% or more, 50% or more, 100% or more, 200% or more than the spacing between the oriented fibers of the first layer. Also, a first layer of oriented fibers in the insulating fabric layer may have a smaller fiber diameter than a fiber diameter of a second layer of oriented fibers in the insulating fabric layer. The diameter of the fibers in the second layer may be greater, by about 20% or more, 50% or more, 100% or more, than the fiber diameter of the fibers in the first layer or oriented fibers in the insulating fabric layer; the first layer may be orthogonal to the second layer. The changes in spacing and size may more effectively reduce radiation and resultant heat flux through the flexible heat barrier.

An insulating fabric layer may have oriented fibers with a spacing between the fibers controlled by a coating, wherein the coating thickness sets the spacing between the fibers. The spacing between fibers may be the coating thickness between fibers or the sum of the coating thickness of each of adjacent fibers. The coating may be any suitable coating and may be continuous around the fibers.

TABLE 1 Estimated Material Cost Max Processing Temperature C Density g/cm3 Density g/cm3 Stength, Mpa Mechanical Resistance cm2/N cm2 of material g/m2 Innegra 150 0.84 0.49 667 1.49E-05 1.096 39.67 S-glass $3.00 850 2.48 1.43 4750 2.10E-06 0.0013 16.44 E-glass $3.00 730 2.54 1.47 2600 3.84E-06 0.0026 30.75 carbon $15.00 3500 1.76 1.02 3530 2.82E-06 0.0019 15.7 basalt $14.89 980 2.7 1.56 4840 2.06E-06 0.0013 17.56 baseline cotton scrim $14.29 204 1.55 0.9 400 2.49E-05 0.018 122.03 aramid $164 450 1.44 0.83 2400 4.26E-06 0.0032 18.89 quartz $300 1070 2.2 1.27 6000 1.67E-0.6 0.0013 11.56 3M Nextel 312 $300 1200 2.8 1.62 1630 6.13E-06 0.0045 54.08 silicon carbide $6,000 1650 3.1 1.79 1625 6.15E-06 0.0045 60.08 This is for just a uni-direction layer. Calclate each ply separately and add weights.

The insulating fabric layer may form a fibrous mat that may be either woven or nonwoven, and the materials of construction may be chosen to best suit the end application by comparing material properties as shown in Table 1. A typical application will consider the maximum processing temperature capability of the material and the cost. Some applications may also need to consider strength. Fire shelters for example must endure extreme winds accelerated by the approaching fire and have typically required fabrics with a tensile strength of at least 157 N/cm (90 lbf/in) or more, or about 210 N/cm (120 lbf/in), like Style 1080 fiberglass fabric from JPS Composite Materials (Anderson SC). The insulating fabric layer or the flexible heat barrier may meet a burst strength requirement as detailed in USDA Forest Service Specification 5100-607D, which specifies (p.6) an average burst strength, for 3 specimens, of not less than 482 kPa (70 psi) when tested per ASTM D 774 and Paragraph 4.4.2.7 of the USDA specification. The insulating fabric layer may consist of woven fibers, unidirectional fibers or randomly oriented fibers depending on the needs of thermal and mechanical properties and the requirements of the coating. The amount of vermiculite, PCM’s, opacifier, intumescent can be interspersed between the fibers, dependent on construction method. Nonwovens have a very high porosity or void volume, such as about 90% or more, therefore there is plenty of volume for other components of the flexible heat barrier. Woven and unidirectional arrays have less porosity and therefore there is less space for coating. FOIL

An exemplary foil is configured as an inner layer or shield side of the flexible heat barrier or fire shelter and is configured to prevent gases from entering the shelter and to reflect radiant energy away from the interior of the fire shelter. An exemplary metal foil has low emittance values and high temperature resistance. A metal foil may be any suitable type of metal including but not limited to, aluminum, copper, gold, platinum, titanium, nickel and iridium. The metal foil may be thin to reduce the weight of the fire shelter and may have a thickness of no more than about 35 µm, no more than about 30 µm and even more preferably less 25 µm, such as about 15 µm or less. A thin metal foil layer is preferred as it reduces weight and bulk of the lightweight multilayer flame barrier. The foil may have an effective low emittance to reduce radiant heat effects. Bare aluminum foil has an emittance of 0.03 µm to 0.05 µm over the IR Wavelength range of wavelengths representing peak radiation for the temperatures of interest. Gold foil has a lower emittance, and withstands higher temperatures but cost limits its applications. Copper foil has low emittance but it oxidizes so readily that its use may be limited to nonoxidizing environments. Although the emittance of titanium foil, which is 0.63, is not outstanding, it could be advantageous if, for example, the fibrous mat was Nextel 440, which has an emittance of 0.87, measured at 25° C. The titanium foil would reduce the radiant heat transfer while offering greater temperature capability of 3000° F. compared to that of aluminum foil of 1220° F. Applying a gold coating by physical vapor deposition to a base lower cost foil, such as titanium foil would provide low emittance of approximately 0.02 at a relatively low cost. Therefore, an exemplary foil includes titanium foil with a lightweight layer of gold attached to the titanium foil, such as by vapor deposition.

The foil may be attached to the fabric layer by an adhesive or by a physical bond, such as by stitching. The adhesive may be a high temperature adhesive such as silicone. The metal foil may be attached to fabric layer with an adhesive that may be a continuous layer or discrete adhesive application, such as adhesive dots. An adhesive may be a fluid that is applied to one or more of the foil and fabric layers being attached. An exemplary adhesive comprises silicone and may be a condensation cured silicone, acetoxy cured silicone, platinum catalyzed cured silicone or a peroxide cured silicone. An adhesive may be diluted with water or solvent prior to application to the lightweight multilayer flame barrier. Also, adhesives with an acceptable decomposition profile, such as poly vinyl acetate, may be considered. Alternatively, the foil may be formed on the fabric by metal spraying with the advantage that adhesives and stitching are eliminated.

Coating Outer Layer

An exemplary flexible heat barrier comprises a coating or coating layer coupled to the insulating fabric layer and forming an exposure side of the flexible heat barrier. The coating may reduce permeability, provide heat capacitance and may scatter or reflect heat from the flexible heat barrier. The coating may have a gas barrier component that reduces the permeability through the coating layer and therefore through the rest of the flexible heat barrier. The coating may have an intumescent component, a component that expands or swells with application of heat to protect the underlayers of the flexible heat barrier. The coating may have an opacifier component that is configured to scatter radiant energy. The coating may have a heat capacitance component such that the ingredients are optimized for maximum heat capacitance to further delay heat flux, or minimized to not retain heat as required by the application. A mixture of these components may be held together by a binder and this binder may couple the coating to the insulating fabric layer.

An exemplary gas barrier component may include a planar of flake type of high temperature material, such as vermiculite. The planar geometry of the vermiculite may effectively reduce the air permeability through the flexible heat barrier. A concentration of the gas barrier component may be used to provide a percentage coverage of the gas barrier component. The gas barrier component may therefore be included in the coating in a weight concentration of about 50% or more, 50% or more or even 75% or more. Vermiculite may be included in the coating in a concentration of about 0.5 g/m², for example and this may form a layer of vermiculite that is about 0.5 µm thick. Note that the concentration may be about 0.5 g/m2 or more, about 0.7 g/m2 or more or even about 1.0 g/m2 or more to provide more permeability reduction from an increased thickness and/or greater coverage of the vermiculite.

In addition, the vermiculite solution serves to suspend the opacifier component and the intumescent component during application without compromising their performance on exposure to fire. An exemplary vermiculite solution is Microlite HTS Vermiculite dispersion from Specialty Vermiculite Corp. of Enoree SC.

An exemplary coating layer may include an intumescent component, a component that expands with application of heat to protect the underlayers of the flexible heat barrier. An exemplary intumescent component is expandable graphite which may be included in a concentration of about 50% or more by weight of the coating. Expandable graphite may be incorporated into the coating because it intumesces endothermically. Not only does it expand, thereby increasing the gap between adjacent materials and the middle layer, but the molecular bonds of the water in the carbon absorb energy as the water is released as steam. The exemplary intumescent component used in the coating described herein is available from Asbury Carbons (Asbury NJ), and have the product code Grade 3626.

The coating may have an opacifier component that is configured to scatter radiant energy. An exemplary opacifier may include high temperature fibers such as silicon carbide fibers. The fibers may have a diameter that is very small such that they are substantially the diameter (within about 50% of the diameter) of the radiant energy wavelength, such as 5 µm or less, about 3 µm or less, about 2 µm or less, about 1 µm or less or even 0.5 µm or less. The size of the silicon carbide fibers may be selected for an application wherein the wavelength of radiation is predicted. Silicon carbide whiskers may provide increased thermal mass without significantly increasing thickness, as well as the capability to reduce radiative heat transfer by optical properties. An exemplary opacifier is C-Tuff SFC Microfibers from Haydale Ceramic Technologies LLC of Greer SC.

The coating may include a binder to hold the components together and this coating may include silicone or another polymeric binder.

For a given application the fabric and foil elements may be chosen first as they determine the minimum areal weight and thickness. For example, in the Example described in Table 2, the fiberglass cloth and foil combination provide the minimal strength and the foil layer on the shield side for reduced emittance, and have a combined thickness of 0.0762 mm (0.003 in) and a weight of 118 g/m² (3.5 oz/yd²). For this specific application, the maximum thickness is 0.228 mm (0.009 in) and maximum weight is 186 g/m² (5.5 oz/yd²). To this foil/fiberglass laminate is added the coating. The coating is optimized to utilize the remaining allowable weight of 67.8 g/m² (2.0 oz/yd²) and thickness 0.1523 mm (0.006 in) to maximize the efficacy of the Flexible heat barrier for this application. For practical reasons in developing the coating, one may start with a preprepared high temperature coating such as the vermiculite coating described above. To this are added the phase change materials, intumescent and opacifiers, in the weights and volumes optimized to maximize performance without exceeding the overall allowance for that layer. Furthermore, these components may be selected for their heat capacitance, in other words if 2 opacifier candidates are available, heat capacitance may be the means by which the opacifier is chosen for a given application. The resulting coating is then applied by known methods, which include spraying, troweling, or by doctor blade, among others.

Flexible Heat Barrier Construction

An exemplary flexible heat barrier has a construction as detailed in Table 2 below:

TABLE 2 Component Description Thickness mm Weight g/m2 Coating vermiculite/SiC/exp. Graphite (50:25:25& binder) 0.1524 67.81 Fabric fiberglass, Stylle 1080 0.0508 46.79 Adhesive foil/cloth bond 0.0076 23.73 Foil aluminum foil 0.0178 48.15 Total 2.286 186.48

The weight of this flexible heat barrier is only 186 g/m².

Flexible Gas Barrier

A flexible gas barrier as described in U.S. Provisional Pat. Application No. 63/298,168, and to U.S. Pat. Applications No. 17/572,619 and 17/916,794, all to Miller, the entirety of each are hereby incorporated by reference herein, may be used in conjunction with the flexible heat barrier described herein for fire shelter applications. The flexible gas barrier (FGB) may provide additional survival time in a fire shelter application but would increase the weight of the fire shelter. An exemplary FGB includes a phase-change material (PCM) and optionally vermiculite in a fibrous matrix, wherein the materials are optimized to reduce the heat flux through the layer. The FGB incorporates two mechanisms to reduce heat flux. The first mechanism is absorption of heat by the PCM or frits, wherein the heat is absorbed as a heat of melting. The second mechanism is reduction of advection or heat flow through the flexible heat barrier. The frits may flow into open spaces of the of the FGB or an adjacent layer to reduce porosity, thereby reducing permeability.

A frit is a ceramic material composition that has been fused, quenched and granulated. Frits may be pulverized pyrometric cone material or pyrometric particles that are coated onto vermiculite to form a FGB layer and may also be incorporated into one or more of the other layers in the flexible heat barrier. Frits or a FGB may be configured between layers of the flexible heat barrier, such as between the coating layer and the insulating fabric, and/or between the insulating fabric and the metal foil. Frits absorb heat as they change from solid to liquid and are selected for the temperature at which they change phase to best reduce overall heat flux by mathematical modeling and experimentation. It may be advantageous to use frits with different melt temperatures in a single layer or to provide a construction consisting of more than one FGB layer wherein different layers use different frits and the overall construction is optimized, through modeling and experimentation, to reduce overall heat flux through the FGB. After the frits absorb heat and melt, the liquid ceramic flows and to reduce permeability through the FGB layer or adjacent layers and may form a seal by spanning any gaps between fibers. This seal reduces or prevents heat flow through the FGB and further reduces heat flux.

The FGB may be configured with the coating or coating layer on or proximal to the exposure side of the flexible heat barrier. The FGB may be a coating on the vermiculite in the coating layer and as the frits melt the intumescent layer expands, it may press the liquid of the melted frits into the openings between the vermiculite. The FGB may be within or part of the insulating fabric layer, which is a structural layer of the flexible heat barrier. The FGB may just be frits that form a coating, and these frits may be combined with fluxes and may be combined with fibers or vermiculite

A frit is a ceramic composition that has been fused, quenched, and granulated. A blue frit includes quartz, lime, a copper compound, and an alkali flux, all heated to a temperature between 850 and 1000° C. Quartz sand may be included in blue frits to contribute silica to the frit. Blue frit includes cuprorivaite (CaCuSi₄O₁₀) crystals and partially reacted quartz particles bonded together by interstitial glass. A green frit is copper-wollastonite ([Ca,Cu]₃Si₃O₉) crystals and a “glassy phase rich in copper, sodium, and potassium chlorides”

A frit may include flux, usually oxides, to lower the high melting point of the main glass forming constituents, usually silica and alumina. A ceramic flux, such as those shown in Table 3, functions by promoting partial or complete liquefaction. The most commonly used fluxing oxides in a ceramic glaze contain lead, sodium, potassium, lithium, calcium, magnesium, barium, zinc, strontium, and/or manganese. Some oxides, such as calcium oxide, flux significantly only at high temperature. Lead oxide is the traditional low temperature flux used for crystal glass, but it is now avoided because it is toxic even in small quantities. It is being replaced by other substances, especially boron and zinc oxides.

TABLE 3 Flux Al2O3 CuO MnO2 SO4 B2O3 Fe2O3 Na2O SrO BaO FeO NiO TiO2 CaO H2O P2O5 V2O5 CO2 K2O PbO ZnO CoO Li2O SiO2 ZrO Cr2O3 MgO SnO2 ZrO2 Cu2O MnO SO3

Ultra-high-temperature ceramics (UHTCs) shown in TABLE 4, may be incorporated as a fiber in the insulating fabric layer or opacifier in the FGB and are a class of refractory ceramics that offer excellent stability at temperatures exceeding 2,000° C. UHTCs may include or consists of borides, carbides, nitrides, and oxides of early transition metals, and heavy, early transition metal borides such as hafnium diboride (HfB₂) and zirconium diboride (ZrB₂), or hafnium nitride (HfN), zirconium nitride (ZrN), titanium carbide (TiC), titanium nitride (TiN), thorium dioxide (ThO₂), tantalum carbide (TaC) and their associated composites.

TABLE 4 Ultra-high Temperature Ceramics Material Formula Crystal structure Lattice parameters (Å) Density (g/cm3) Melting point a b c (°C) (°F) Hafnium carbide HfC FCC 4.638 4.638 4.638 12.76 3958 7156 Tantalum carbide TaC Cubic 4.455 4.455 4.455 14.5 3768 6814 Niobium carbide NbC Cubic - - - 7.82 3490 - Zirconium carbide ZrC Cubic 4.693 4.693 4.693 6.56 3400 6152 Hafnium nitride HfN FCC 4.525 4.525 4.525 13.9 3385 6125 Hafnium boride HfB2 Hexagonal 3.142 - 3.476 11.19 3380 6116 Zirconium boride ZrB2 Hexagonal 3.169 - 3.53 6.1 3245 5873 Titanium boride TiB2 Hexagonal 3.03 - 3.23 4.52 3225 5837 Titanium carbide TiC Cubic 4.327 4.327 4.327 4.94 3100 5612 Niobium boride NbB2 Hexagonal 3.085 - 3.311 6.97 3050 0 Tantalum boride TaB2 Hexagonal 3.098 - 3.227 12.54 3040 5504 Titanium nitride TiN FCC 4.242 4.242 4.242 5.39 2950 5342 Zirconium nitride ZrN FCC 4.578 4.578 4.578 7.29 2950 5342 Silicon carbide SiC Polymorphic - Various - 3.21 2545 4613 Vanadium carbide VC Cubic - - - 5.77 2,810 unstable - Tantalum nitride TaN Cubic 4.33 4.33 4.33 14.3 2700 4892 Niobium nitride NbN Cubic - - - 8.47 2573 - Vanadium nitride VN Cubic - - - 6.13 2,050 unstable ? -

A flexible gas barrier (FGB) may include a vermiculite layer to reduce advection more quickly. Based on experiments, it takes a few seconds for the PCM’s to melt, flow and seal. By incorporating vermiculite into the FGB, advection can be temporarily reduced in the FGB from the beginning of the exposure. When vermiculite is added to the FGB, a solution may be formed as taught by U.S. Pat. No. 3,325,340 to G. Walker during the FGB manufacture to form a barrier against advection which is effective from the initial exposure. By blocking advection, heat is retained within the FGB, and this accelerates the phase change of the PCM’s enhancing overall performance. These FGB’s are intended for moderate and high temperatures where ceramics can be used as PCM’s. Fibers of fiberglass, silica, mullite, alumina, silicon carbide, or others listed in Table 4 could be used to form a substrate for the FGB, wherein the fibers may be woven, unidirectional or randomly oriented as in a nonwoven. A binder could be added to hold the FGB materials in a layer form until exposure. FGB thickness could be 0.1 mm to 5 mm. The FGB could be made by producing a slurry which could be cast and made into a free-standing layer or applied to a substrate.

The summary of the invention is provided as a general introduction to some of the embodiments of the invention, and is not intended to be limiting. Additional example embodiments including variations and alternative configurations of the invention are provided herein.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the principles of the invention.

FIG. 1 shows a perspective top view of a fire shelter.

FIG. 2 shows several prototype fire shelters evaluated during development of the M2002

FIG. 3 shows a graph of Temperature And Heat Flux Comparison, With And Without FGB.

FIG. 4 shows a diagram of the layers of an exemplary fire shelter, lay-up #2, compared with two other lay-ups, including the M2002 fire shelter and another experimental lay-up, Lay-up #1.

FIG. 5 shows the Meker Burner test results for duration for the fire shelter lay-ups depicted in FIG. 4 .

FIG. 6 shows a graph of Meker burner results for two fire shelter lay-ups containing an FGB that offer significantly improved habitability compared to the M2002, for which data is also plotted.

FIG. 7 shows a cross-sectional diagraph of an exemplary middle layer having a fabric configured between and integrally coupled to a coating on the hot side, and a foil on the cold side.

FIG. 8 shows a prospective view of an exemplary insulating fabric layer having layers of oriented fibers configured orthogonally to each other.

FIG. 9 shows the results of Meker burner tests for three-layer fire shelter systems including a middle layer as depicted in FIG. 8 with the construction as described herein.

FIG. 10 shows photographs of the shield side of the flexible heat barrier following a Meker burner test.

FIG. 11 shows photographs of the exposure side of the flexible heat barrier following a Meker burner test.

FIG. 12 shows a graph of emittance values for foil over wavelength of interest for a fire shelter application.

FIG. 13 shows a graphical model of radiant heat transfer through a polarizing fiber array.

FIG. 14 , FIG. 15 and FIG. 16 show a graphical model of the effect of a polarizing fiber array with varying gap distances between the oriented fibers.

FIG. 17 shows a chart of transmittance, reflectance and absorption through a polarizing fiber array.

FIG. 18 shows a diagram of a woven fabric that may be a layer or component of the insulating fabric layer

Corresponding reference characters indicate corresponding parts throughout the several views of the figures. The figures represent an illustration of some of the embodiments of the present invention and are not to be construed as limiting the scope of the invention in any manner. Some of the figures may not show all of the features and components of the invention for ease of illustration, but it is to be understood that where possible, features and components from one figure may be an included in the other figures. Further, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Also, use of “a” or “an” are employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

Certain exemplary embodiments of the present invention are described herein and are illustrated in the accompanying figures. The embodiments described are only for purposes of illustrating the present invention and should not be interpreted as limiting the scope of the invention. Other embodiments of the invention, and certain modifications, combinations and improvements of the described embodiments, will occur to those skilled in the art and all such alternate embodiments, combinations, modifications, improvements are within the scope of the present invention.

Referring now to FIGS. 1 and 2 , a fire shelter forms a top shielding surface or enclosure and is configured to fit into a compact space, such as a backpack. The fire shelter is configured to be folded and configured in the backpack. The image of the backpack is not to scale. As shown in FIG. 2 a plurality of fire shelters can be deployed to form a protective dome over each firefighter in a group.

As shown in FIG. 3 instantaneous heat flux in forced convection environment can be greatly reduced by the addition of a Flexible Gas Barrier (FGB) layer. FIG. 3 compares instantaneous heat flux, Qinstant and temperatures in two locations over a 60 second exposure for insulation systems with and without the FGB. The system with the FGB indicates significantly lower heat flux resulting in significantly lower temperatures at both locations measured.

A flexible gas barrier (FGB #28), a ceramic paper with a phase change material including frits and vermiculite, was developed for use as the middle layer in a fire shelter lay-up shown in FIG. 4 . flexible heat barrier

The weights and thicknesses of the materials in the three constructions of FIG. 4 as well as a Phase 1 target are tabulated in Table 5.

TABLE 5 M2002 Lay-up #1 Lay-up #2 FGB#28 Phase 1 Target Outer g/m2 434 301.8 301.8 301.8 Middle g/m2 n.a. n.a. 115.3 186.5 Inner g/m2 94.9 94.9 94.9 94.9 Total Shelter Wall g/m2 528.9 396.7 512 583.2 Floor kg 0.531 0.390 0.390 0.390 Seams kg 0.086 0.086 0.086 0.086 Complete Shelter, kg 1.99 1.51 1.81 1.99 Wall Thickness, mm 0.762 0.584 0.914 0.991

Also, the thermal performance of these constructions was tested and plotted in FIG. 5 , where the intersection of the calorimeter temperature data with the Stoll curve predicts the fire shelter failure due to second degree burns on the occupant. As shown from the weights in Table 5 and the Meker burner test results in FIG. 5 , increasing wall weight improves performance and delays second degree burns. It can also be seen that the performance of the M2002 was matched by lay-up #2, which is 10% lighter than the M2002. The Flexible Gas Barrier (FGB #28) layer was used as the MIDDLE layer in lay-up #2, and provided equivalent performance to the M2002 construction at a lighter weight.

As shown from the weights of the components in Table 5 and the Meker burner test results in FIG. 5 , increasing weight improves performance and delays second degree burns. It can also be seen that the performance of the M2002 was matched by lay-up #2, which is 10% lighter than the M2002. This suggests that an insulating fabric layer that is slightly heavier than FGB #28 can be successfully utilized to increase fire shelter habitability by 20% without increasing overall weight or bulk. In these tests, a Flexible Gas Barrier (FGB) layer was configured between fabric laminates similar to those currently used in the M2002.

The insulating fabric layer may be specifically optimized to increase time to second degree burn, or shelter protection time. In an exemplary embodiment, an improvement of about 20% (~11 second) over M2002 is realized with no increase in weight or bulk over M2002. This improvement will produce a fire shelter with improved efficacy resulting in fewer injuries and deaths for firefighters and support personnel. The cost of an exemplary fire shelter of the present invention may be maintained to a marginal amount over the cost of the M2022 fire shelter, such as no more than about $100 per shelter, or even no more than $85 per shelter.

As shown in FIG. 6 , research and development further confirmed that a FGB layer that meets the weight and thickness constraints of the proposed fire shelter design and also increased survivability by 20%. The Meker burner test data confirms that the M2002 is survivable for 54 seconds in the controlled test, and the flexible heat barrier with the FGB configured between the coating and the foil layer increases survivability to 64 seconds, representing a 20% improvement. FGB - #1 and FGB - #2 are plots of data from two separate runs of the same FGB material, meant to indicate the repeatability of the results. Of course, full shelters would need to be constructed and tested to confirm the suitability of other aspects of the design.

An exemplary fire shelter of the present invention meets the following qualifications:

-   a. Maintain radiant heat protection of the current M2002 fire     shelter -   b. Improve protection in direct flame contact -   c. Maintain the requirement that users not be exposed to dangerous     toxic compounds from the shelter -   d. Maintain the strength and durability of the current M2002 fire     shelter -   e. Prevent flammable gasses from collecting inside the fire shelter -   f. Maintain the weight and bulk of the current M2002 fire shelter -   g. Marginal to no increase in cost over the M2002 fire shelter.

As shown in FIG. 7 , an exemplary flexible heat barrier 30 comprises an insulating fabric layer 60 with a coating 40 configured on an exposure side 24, and a metal foil 80 configured on a shield side 26. Could be 90 except we use that later. As described herein the coating 40 is configured to reduce heat transmittance, while the insulating layer is configured to provide structural support and insulate the shield side from heat and the metal foil is configured to reduce heat radiated from the cold side and provide a gas barrier.

As described herein, the insulating fabric layer may comprise two or more layers of high-temperature, oriented fibers. The layers may have the oriented fibers oriented orthogonally to each other, or within about 20 degrees of orthogonal to polarize the radiant energy. A thin layer of optically transparent material, like a nonwoven alumina mat, or woven quartz scrim may be used to thermally isolate the layers of oriented fibers without significantly interfering with the polarization process. An adhesive 50 may be used to bond the metal foil layer to the insulating fabric layer. The coating layer 40 may include a binder 45 that adheres the coating to the insulating fabric layer. Table 2 shows the construction of an exemplary flexible heat barrier shown in FIG. 7 .

The coating 40 includes an intumescent component 42, a gas barrier component 44, such as vermiculite and an opacifier component 46 held together by the binder 45. The ratio of these components may be selected as described herein to provide effective heat shielding properties and survival time.

A flexible gas barrier (FGB) 90 is configured with the flexible heat barrier 30 and contains a gas barrier 44′, such as vermiculite 94 and pyrometric particles 91 comprising frits 92, fluxes 93 that are configured to melt at prescribed temperature to flow and fill spaces between the gas barrier material. As described herein, the FGB may be a coating configured with one or more of the layers of the flexible heat barrier or may be a separate layer configured on or between the fibers of the layers, such as between the coating 40 and insulating fabric layer 60 or between the insulating fabric layer and the foil 80.

As shown in FIG. 8 , an exemplary insulating fabric layer 60 includes a first layer 66 of fibers 62 that are oriented fibers 64 and a second layer 68 with oriented fibers that are configured orthogonally to the oriented fibers in the first layer. As described herein, this arrangement of oriented fibers with a very small fiber gap may effectively polarize radiant energy to better insulate the shield side of the flexible heat barrier. As described herein, the fibers may be small in diameter, and the gaps between the parallel or oriented fibers may be substantially the same as the wavelength of the peak radiant energy.

FIG. 9 shows the results of a Meker burner test for three three-layer fire shelter systems with weights and thickness predicted in Table 5 for the Phase I target, and better performance than anticipated in FIG. 5 for the Phase I target. The Meker Burner test shows the intersection of the calorimeter temperature data with a Stoll curve and therefore predicts the fire shelter failure due to 2^(nd) degree burns on the occupant. This lay-up includes the flexible heat barrier described in Table 2 used in place of FGB #28 in the configuration shown for lay-up #2 in FIG. 4 . FIG. 9 shows that each of the flexible heat barriers tested had a survival time of 86 seconds. The flexible heat barrier middle layer increases survivability to 86 seconds in the Meker burner test, which represents a 59% improvement over the M2002. The construction of the present flexible heat barrier for a fire shelter application is expected to be more commercially viable than the technology described in U.S. Pat. No. 10,099,450 because the vermiculite dispersion is not relied upon for adhering the foil to the insulating fabric layer. Lastly, the distinct layers of the flexible heat barrier each provide a unique benefit, wherein the insulating fabric layer provides added strength, the foil provides a low emittance and the coating absorbs heat while the intumescent component expands with exposure to heat.

FIGS. 10 and 11 show the fire shelter layers after Meker Burner testing. The exposure side 24 was exposed to the burner during this testing. FIG. 10 shows the shield side of a flexible heat barrier, the side that would be exposed to the fire fighter in a fire shelter application. As can be seen, it’s in good condition even after providing 86 seconds of protection. In FIG. 11 , the exposure side shows delamination, as is typical with severe exposures such as this. Also, the intumescent component 42 has intumesced on the exposure side. Since the test only exposes a circular section in the middle of the 15.24 cm square samples, unexposed material, as it would appear in an unused fire shelter, may be seen outside of the central area.

FIG. 12 shows a graph of emittance values for foil over wavelength of interest for a fire shelter application.

Referring now to FIGS. 13 to 17 , an insulating fabric layer 60 with a polarizing array of fibers 62, can effectively polarize radiant energy. As shown in FIG. 13 , oriented fibers 64 with diameters 63 and a gap distance 65 between the fibers may be sized with gaps that approach the wavelength 67 of the radiant energy. When the gap distance is the same or smaller than the wavelength of the radiant energy, the radiant energy will be polarized as it passes through the oriented fibers 64. As shown in FIG. 14 to FIG. 16 , the diameter of the fibers and again the gap distance between them will affect the polarization of the light. A gap distance greater than, equal to and smaller than the wavelength of radiation (1 micron) are modeled. Diagram 14 represents a fiber diameter of 0.6 microns and a gap distance of 2.0 microns, greater than the wavelength of the radiation. Diagram 15 represents a fiber diameter of 0.6 microns and a gap distance of 1.0 microns, equal to the wavelength of the radiation. Diagram 16 represents a fiber diameter of 0.6 microns and a gap distance of 0.5 microns, smaller than the wavelength of the radiation. FIG. 17 shows the percent vertical polarization along a line parallel to the fiber-line on the transmitted side of the fibers. The results shows that the fibers do polarize the unpolarized incident radiation. Polarization of the radiation occurs to a greater extend when the gap distance is equal to or smaller than the wavelength of radiation. Polarization of the radiation up to 40 to 50% was predicted for the smallest gap distance spacing of 0.5 um.

As shown in FIG. 18 , a woven fabric 67 may be a layer or component of the insulating fabric layer 60 and may include a first set of oriented fibers 64, and a second set of oriented fibers 64′. The first set of oriented fibers 64 in the weave may be a different type of fiber from the second set of oriented fibers 64′. The woven fabric includes fibers 62 that may be selected from high temperature fibers as described herein, such as polarizing silicon carbide fibers, quartz fibers, glass fibers and the like. The warp fibers may be one type of fiber while the fill fibers or yarns may be a second type of fiber. The fibers may also include opacifier powders, fibers and/or frits that are powders or fibers and configured to melt and flow to seal off gaps in the weave. The weave may be a plain or basket weave, twill weave, satin weave, or leno weave. A frit fiber may be only a portion of the yarn or strand in the weave. In an exemplary embodiment a first set of fibers or yarns, the warp yarns, comprise polarizing silicon carbide fibers and a second set of fibers or yarns, the weft yarns, comprise optically transparent quartz fibers in a plain, satin, basket, twill or leno weave. The weave and the denier of the weft fibers may be selected to maintain the desired spacing between the polarizing fibers, such as silicon carbide fibers.

A coating 78 may be configured on and/or around the fibers to create the spacing between the fibers. The spacing may be the thickness of the coating between the fibers or the combined thickness of a coating on adjacent fibers. The coating may be continuous around the fibers forming a continuous layer or discontinuous.

It will be apparent to those skilled in the art that various modifications, combinations and variations can be made in the present invention without departing from the scope of the invention. Specific embodiments, features and elements described herein may be modified, and/or combined in any suitable manner. Thus, it is intended that the present invention cover the modifications, combinations and variations of this invention provided they come within the scope of the appended claims and their equivalents. 

What is claimed is:
 1. A flexible heat barrier comprising: a) an insulating fabric layer comprising high temperature fibers having a melt temperature of at least 800° C.; b) a coating coupled to said insulating fabric layer and configured as an outer layer of the flexible heat barrier and comprising: i) an intumescent component; ii) an opacifier component; iii) a gas barrier component; and iv) a binder component; c) a metal foil coupled to said insulating fabric layer and configured as an inner layer of the flexible heat barrier; wherein the outer layer is configured as an exposure side of the flexible heat barrier and configured to be exposed to a heat source or a flame and the inner layer is configured as a shield side away from said heat source or flame; and wherein the flexible heat barrier has an average burst strength of at least 482 kPa (70 psi) according to American Standard Test Method (ASTM) 774 and United States Department of Agriculture (USDA) specification paragraph 4.4.2.7.
 2. The flexible heat barrier of claim 1, wherein the insulating fabric layer is a polarizing fabric layer comprising a layer or oriented high temperature fibers having a spacing between said oriented fibers of 5.0 µm or less.
 3. The flexible heat barrier of claim 2, wherein the spacing between said oriented fibers is 2.0 µm or less.
 4. The flexible heat barrier of claim 2 wherein the oriented fibers comprise a coating and wherein the coating forms said spacing between the oriented fibers.
 5. The flexible heat barrier of claim 1, wherein the insulating fabric layer comprises two layers of oriented high temperature fibers, each having a spacing between said oriented fibers of 5.0 µm or less.
 6. The flexible heat barrier of claim 5, wherein a first layer of oriented high temperature fibers is configured substantially orthogonally, within about 20 degrees or less of orthogonal, to a second layer of oriented high temperature fiber.
 7. The flexible heat barrier of claim 5, wherein the second layer of oriented high temperature fibers is configured more proximal to the inner layer and has a larger spacing between said oriented fibers by at least 20% than said spacing between said oriented fibers of the first layer of said oriented fibers.
 8. The flexible heat barrier of claim 7, wherein the second layer of oriented high temperature fibers has a larger fiber diameter, by at least 20%, than a fiber diameter of the first layer of said oriented fibers.
 9. The flexible heat barrier of claim 5, wherein the second layer of oriented high temperature fibers has a larger fiber diameter, by at least 20%, than a fiber diameter of the first layer of said oriented fibers.
 10. The flexible heat barrier of claim 2, wherein the insulating fabric layer comprises woven oriented fibers.
 11. The flexible heat barrier of claim 1, wherein insulating fabric layer comprises high temperature polymers having a melt temperature of 300° C. or more.
 12. The flexible heat barrier of claim 11, wherein insulating fabric layer comprises polyimide.
 13. The flexible heat barrier of claim 1, wherein insulating fabric layer comprises fibers having a melt temperature of 800° C. or more.
 14. The flexible heat barrier of claim 1, wherein insulating fabric layer comprises inorganic fibers selected from the group consisting of: glass, fiberglass, silicon carbide and mullite, alumina, quartz.
 15. The flexible heat barrier of claim 1, wherein the foil comprises a first layer of foil and second layer of foil, wherein the first layer of foil has an emissivity that is at least 20% higher than an emissivity of said second layer of foil.
 16. The flexible heat barrier of claim 1, wherein the foil comprises gold layer.
 17. The flexible heat barrier of claim 16, wherein the gold layer is a vapor deposition gold layer having thickness of no more than about 1500 µm.
 18. The flexible heat barrier of claim 16, wherein the foil comprises titanium foil.
 19. The flexible heat barrier of claim 18, wherein the foil comprises a gold layer on said titanium foil.
 20. The flexible heat barrier of claim 1, wherein the intumescent component comprises expandable graphite. 